Not applicable.
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Not applicable.
The invention presented here involves an anti-skid device and process for a vehicle with a hydrostatic transmission.
It is also intended for vehicles with hydrostatic transmissions provided with this anti-skid device.
Vehicles with hydrostatic transmissions are vehicles whose driven wheels are driven by hydraulic motors. The thermal engine of these vehicles is coupled to a hydraulic pump; this pump is itself connected to each of the hydraulic motors, which drive the wheels, where these wheels themselves ensure that the vehicle is driven. In order to ensure the differential effect between the wheels, the effect necessary so that the speed of the wheels can independently adapt to the situation of the vehicle in curves, the hydraulic motors are connected, generally in parallel, on the hydraulic pump. This differential makes it possible to drive the driven wheels at different rotational speeds, for example, in curves or when their pneumatic tires have inequalities of inflation, wear and tear, or load, while thus allowing these wheels to adapt to the conditions of speed and to adhesion that they encounter.
In hydraulic transmissions, in order to obtain the differential effect, it is made certain that the motors of the wheels, whether for the transmissions having two driven wheels, three driven wheels, four driven wheels, six driven wheels, etc., are all connected in parallel. This hydraulic assembly allows a differential effect between all of the driven wheels.
When the adhesion is not sufficient on one wheel, the differential effect automatically makes it so that it skids, due to the fact that it begins to turn more quickly than the speed at which it would have to turn if the adhesion were normal.
The object of the invention is thus a device and a process that allows a vehicle with a hydrostatic transmission with at least two driven wheels to prevent the skidding of the wheels while maintaining the differential effect between the driven wheels.
An anti-skid device for vehicles with a hydrostatic transmission that has an electronic control is known from the prior-art; moreover, this device has been used by the applicant until now.
In the example of the application of this known device to the equipment of a four-wheel vehicle with two driven wheels, this device consists of a speed sensor on each driven wheel and at least one speed sensor on a non-driven wheel. On the other hand, the vehicle is also provided with a direction angle sensor and a hydrostatic transmission with a pump having a variable output connected in parallel to two hydraulic motors of driven wheels. These different sensors are connected to a computer. This computer calculates the theoretical speed at which each of the driven wheels must turn. To do this, it uses the data of the speed sensors of the non-driven wheels as well as the data of the direction angle sensor.
A diagram of the vehicle and the rolling circumference of its wheels are data programmed in the memory of the computer. At each moment, the computer compares the theoretical calculated speed of each of the driven wheels with their actual speed measured by their own sensors, whether in a straight line, in a curve, moving forward, or moving in reverse. When the actual speed of at least one driven wheel is greater than its theoretical speed, the computer determines that skidding is involved. From then on, the computer acts on a valve for limiting the proportional output coupled to the hydraulic motor of each of the wheels, in a manner so as to reduce the excess speed of the wheel that is skidding to the theoretical speed.
This device, however, has the major disadvantage of reacting with a delay. In fact, it is necessary for the wheel to have already started skidding so that the computer detects the skidding, and commands a corrective procedure. The wheel has already started at excess speed when the proportional valve acts in order to reduce the speed to the theoretical speed. The consequences are such that the wheel that skids has already dug a hole in the ground due to the skidding. The hole thus dug, even if the wheels no longer skid, can cause severe mobility problems.
In addition, the obligatory use of wheel sensors makes necessary the passage of electric cables near the wheel hubs which is another serious disadvantage when the machines work in the ground.
The device and the process, the object of the invention, have the purpose of preventing any possibility of skidding and thus preventing the wheels from digging holes causing the immobilization of the vehicle.
The device according to the invention applicable to vehicles with a hydrostatic transmission provided with at least one sensor fitted to transmit data making it possible to calculate the output of the hydrostatic transmission, from a direction angle sensor and an electronic computer that uses the data of these sensors in order to calculate the theoretical output of the hydraulic motors of the driven wheels of these vehicles and, as a result, the theoretical speed of these wheels, is mainly notable in that the sensors are scanned at very close intervals, for example every ten milliseconds, by the computer programmed in order to adjust, at each scanning, the hydraulic outputs of the output regulators by the electric control coupled to each hydraulic motor of the driven wheel, in a manner so as to limit the output of each output regulator to a value slightly greater than the theoretical output, determined by the computer, of the motor of the wheel to which this output regulator is coupled.
According to anti-skid process of the invention applicable to vehicles with a hydrostatic transmission provided with at least one sensor fitted to transmit data making it possible to calculate the output of the hydrostatic transmission, from a direction angle sensor and an electronic computer parameterized so that it uses the data of these sensors in order to calculate the theoretical output of the hydraulic motors of the driven wheels of these vehicles and, as a result, the theoretical speed of these wheels, the sensors are scanned at very close intervals, for example every ten milliseconds, by the electronic computer used in order to adjust, at each scanning, the hydraulic outputs of the output regulators by the electric control coupled to each hydraulic motor of the driven wheel, in a manner so as to limit the output of each output regulator to a value slightly greater than the theoretical output, determined by the computer, of the hydraulic motor of the wheel to which this output regulator is coupled.
The process and the device of the invention prevent any instantaneous runaway and eliminate any possibility for appreciable skidding of the driven wheels of the vehicle, regardless of the number of driven wheels of the vehicle, its direction of movement (straight line, in a curve, in forward, in reverse) and the type of surface on which it is moving.
The output of each output regulator can be limited to a value corresponding to a wheel speed of 0 to 10% and, preferably, from 3 to 4% greater than the theoretical speed of each of the driven wheels.
In the hypothesis where a wheel is in a skidding situation, it can only skid from 3 to 4% relative to its theoretical speed. This skidding, if it is produced, is thus insignificant and does not cause any transmission problems.
Taking into account the fact that the output regulators are regulated at 3 to 4% above their theoretical value, the hydraulic circuit of the hydrostatic transmission functions in normal conditions. The device does not generate any high pressure. The efficiency of this system is identical to that of a system that does not have anti-skid. This system does not depend on the response time of the electronics or the regulators, thus there is no actual skidding.
The anti-skid device according to the invention also has the advantage that it can be used as a hydrostatic brake for engines having four driven wheels, when they are on slopes. In fact, on large slopes when the load is transferred a great deal onto the front wheels, the computer will determine this situation and, in case of braking, the output regulators will regulate an output a few percent less than the theoretical speed; i.e. the output regulator will constantly brake the wheels. This solution prevents the less loaded rear wheels of the vehicle from locking or turning in the reverse direction.